While the present invention has application to various electronic devices requiring current control, the advantages of the operation of the invention will be well understood from a description of its operation with boost converters. For this reason, a brief discussion of the operation of prior art boost converters will facilitate the understanding of the invention.
FIG. 1 shows an electrical schematic of a prior art power electronic circuit for a power factor corrected boost converter. A boost converter takes an input DC voltage V.sub.in and produces an output DC voltage V.sub.out having a higher voltage level. As illustrated in FIG. 1, V.sub.in input to boost converter 10 is the rectified output from diode bridge 12, which is supplied power from an alternating voltage source 14. Within the boost converter 10, V.sub.in is applied to one end of an inductor L1 whose output is connected to diode D1 and power electronic switch IGBT. A capacitor C1 is shunted across the output of the diode and V.sub.out is taken from point 16. The power electronic switch IGBT, placed in series with V.sub.in and L1 when IGBT is closed, is controlled by gate drive 18, and controls the current through the inductor L1. A control signal is provided to gate drive 18 to control the switch IGBT.
The operation of the boost converter 10 is as follows. The power electronic switch IGBT is turned on by gate drive 18, which causes current to flow through the switch as indicated by the arrow A, and inductor L1 is impressed with V.sub.in. The current through inductor L1 gradually increases in response to V.sub.in at a rate that is determined by V.sub.in =L1*di/dt and the magnetic field of the inductor becomes charged due to the increasing current. The switch IGBT is then turned off by gate drive 18, causing diode D1 to conduct. The inductor L1 then discharges into the capacitor C1 through diode D1, charging the capacitor C1. Output voltage 16 may be taken off the circuit between diode D1 and capacitor C1.
The power electronic switch IGBT is controlled independently of the input voltage V.sub.in and thus the input current entering the boost converter may be controlled by control of the switch IGBT. If V.sub.in is full wave rectified AC, then the gate control signal may be selected to produce a desired input current waveform matching the input voltage and thereby having unity power factor.
The waveform of the input current is illustrated in FIG. 2b, while the gate control voltage is shown in FIG. 2a. When the gate voltage is high, the switch IGBT is closed, allowing current to increase in the inductor(as shown at 19a). The input current to the boost converter, measured at current sensor 3 thus rises while the switch IGBT is closed. The current continues to rise until the switch IGBT is opened when the gate voltage switches to low. The current then decreases (as shown at 19b) as the inductor discharges through D1 into C1. As can be seen from FIGS. 2a and 2b, in the early part of the cycle, the gate voltage is high longer than it is low, and thus the current rises more than it falls. With appropriate choice of the pulse widths of the gate voltage, a desired current waveform may be produced. A simulated sinewave SS is shown in FIG. 2b, with the current bounded by an upper hysteresis limit UHL and a lower hysteresis limit LHL.
The manner of selection of the prior art gate control pulsed waveform is indicated in the electrical schematic of FIGS. 3A, 3B, 3C, 3D and 3E. The ac voltage produced by the utility from which the power is drawn is sampled by V.sub.ac sensor 1, also shown in FIG. 1. FIG. 3B shows the voltage waveform appearing at B in FIG. 3A. This voltage is rectified in rectifier 22 to produce a half-wave rectified sine wave signal C (illustrated in FIG. 3C). The actual output voltage is sensed at V.sub.dc sensor 2 and compared with desired V.sub.dc using amplifier 24 to produce output signal F which represents the deviation of the DC output from a desired V.sub.dc. V.sub.dc is a constant that is determined by the end use requirements. Signal C and Signal F are multiplied in multiplier 26 to establish a desired current waveform designated as signal G. Signal G is compared with a voltage representation of the current signal E (FIG. 3E) sensed at current sensor 3 using hysteresis comparator 28 and the output of comparator 28 signal D (FIG. 3D) is used as the control signal for the gate drive 18.If the actual current waveform exceeds the desired current waveform (signal G) by more than a set amount, the comparator will generate a control signal which, while on, will cause the current in inductor L1 to decrease. When the actual current waveform is below the desired current waveform by more than a set amount, the comparator will generate a control signal which, while on, will cause the current in inductor L1 to increase. For the gate drive 18 and switch IGBT shown, the current increase signal closes the switch IGBT, while the current decrease signal opens the switch IGBT. This hysteresis loop is continuous and maintains the input current waveform closely tied (within a hysteresis deadband) to the input voltage waveform.
The inventor is aware of three custom chips that provide the control outlined in FIGS. 1, 2a, 2b and 3, namely UC3854 provided by Unitrode Integrated Circuits Corporation of Merrimack, NH, USA; ML4812 provided by Micro Linear Corp of San Jose, Calif., USA and LT1248 provided by Linear Technology Corporation of Milipitas, Calif., USA. These chips periodically set the gate control and reset when the current reaches the required value. The circuitry illustrated in FIG. 3 is contained within an integrated circuit, and receives input from various sensors referred to there. Further description of these products can be found in the product monographs provided by these companies.
The inventor has provided a new way of providing the gate control for a boost converter, but the invention also may be applied to control voltage and current in other switch mode circuit applications, such as flyback and buck converters. The circuit is simpler than the integrated circuits known to the inventor, much less expensive, and requires less filtering to remove the ripple generated by the switching of the switch IGBT.
Thus in one embodiment of the invention there is provided a current controller for controlling an input current carried by a primary conductor, the current controller comprising a gapped core of magnetic material magnetically coupled to the primary conductor, as for example by the primary conductor being wound around the core, a secondary conductor magnetically connected to the core of magnetic material in an opposite manner to the primary conductor such that current flowing in the secondary conductor generates a second magnetic field in the core opposed to the first magnetic field; and a Hall effect latch located in the air gap and having output voltage corresponding to a hysteresis function of the difference in the first and second magnetic fields.
An example of a hysteresis function for the voltage is a function in which the voltage can take on one of two different levels for any given value or level of the magnetic field between an operate point and a release point. In effect, the voltage may have a defined level while the magnetic field is rising between two magnetic field levels, and a different defined level when the magnetic field is falling between two magnetic field levels.
Such a current controller has particular application for use with a boost converter having a gate drive in which the output of the Hall effect latch is connected to the gate drive. The secondary conductor is preferably connected to a desired current waveform generator and is wound around the core a number of times.
The Hall effect latch preferably includes a Hall effect device, an amplifier connected to the Hall effect device, and a hysteresis comparator connected to the output of the amplifier.